System and method for providing control for switch-mode power supply

ABSTRACT

System and method for providing control for switch-mode power supply. According to an embodiment, the present invention provides a system for regulating a power converter. The system comprises a signal processing component that is configured to receive a first voltage and a second voltage, to process information associated with the first voltage and the second voltage, to determine a signal based on at least information associated with the first voltage and the second voltage, and to send the signal to a switch for a power converter. The switch is regulated based on at least information associated with the signal. The signal processing component is further configured to determine the signal to be associated a first mode, if the first voltage is higher than a first threshold.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority to Chinese Patent Application No.200610030188.X, filed Aug. 16, 2006, entitled “System and method forproviding control for switch-mode power supply”, by inventors Jun Ye,Zhen Zhu, Shifeng Zhao, Zhiliang Chen, and Lieyi Fang, commonlyassigned, incorporated by reference herein for all purposes.

BACKGROUND OF THE INVENTION

The present invention is related to integrated circuits. Morespecifically, the present invention can be applied to controllers usedfor switch mode power supply. According to various embodiments, thepresent invention provides various power control schemes to reducestandby power consumption and improves system efficiency. Merely by wayof example, the present invention can be used in switch mode powerconversion system including, among, other things, offline fly-backconverters and forward converters. It is to be appreciated that thepresent invention has a broad range of applications.

Power converters are widely used in various applications, such asproviding power to portable consumer electronics. The power converterscan convert electric power from one form to another form. As an example,the electric power is transformed from alternate current (AC) to directcurrent (DC), from DC to AC, from AC to AC, or from DC to DC.Additionally, the power converters can convert electric power from onevoltage level to another voltage level.

In the past various types of power converters have been developed. Forexample, linear regulators have traditionally been used for powerconverters. A linear regulator is a voltage regulator based on an activedevice (such as a bipolar junction transistor, field effect transistoror vacuum tube) operating in its “linear region” or passive devices likezener diodes operated in their breakdown region. The regulating deviceis made to act like a variable resistor. While linear regulators havebeen used for many years, their power efficiency is often inadequate forportable electronics. For example, due to low power efficiency, linearregulators often waste large amount of energy and generate excessiveheat for portable devices.

With the advent of integrated circuits, switched-mode power supply hasbeen invented and utilized for various applications. Switch mode powersupplies are typically implemented with a switching regulator, which isan internal control circuit that switches the load current rapidly onand off in order to stabilize the output voltage. For certainapplications, switch-mode power supply uses pulse-width-modulated (PWM)or pulse-frequency-modulated (PFM) mechanism. These mechanisms areusually implemented with a switch-mode-controller including variousprotection components.

In recent years, power systems are often required to comply withstandards for energy consumption. For example, various internationalorganizations have imposed energy saving standards such as “EnergyStar”, “Blue Angel”, etc. For example, such standards imposerequirements that, among other things, power supplies have low standbypower consumption (i.e., high power efficiency under very light or zeroload condition).

In the past various techniques have been developed to lower variousforms of power consumption. For example, different types of standbypower consumption schemes have been developed. Unfortunately,conventional techniques are often inadequate.

Therefore, it is desirable to have improved systems and methods forpower systems.

BRIEF SUMMARY OF THE INVENTION

The present invention is related to integrated circuits. Morespecifically, the present invention can be applied to controllers usedfor switch mode power supply. According to various embodiments, thepresent invention provides various power control schemes to reducestandby power consumption and improves system efficiency. Merely by wayof example, the present invention can be used in switch mode powerconversion system including, among, other things, offline fly-backconverters and forward converters. It is to be appreciated that thepresent invention has a broad range of applications.

According to an embodiment, the present invention provides a system forregulating a power converter. The system comprises a signal processingcomponent that is configured to receive a first voltage and a secondvoltage, to process information associated with the first voltage andthe second voltage, to determine a signal based on at least informationassociated with the first voltage and the second voltage, and to sendthe signal to a switch for a power converter. The switch is regulatedbased on at least information associated with the signal. The signalprocessing component is further configured to determine the signal to beassociated a first mode, if the first voltage is higher than a firstthreshold. If the first voltage is lower than a second threshold and thesecond voltage is higher than a third threshold, the signal processingcomponent determines the signal to be associated with a second mode. Ifthe first voltage is lower than the second threshold and the secondvoltage is lower than the third threshold, the signal processingcomponent determines the signal to be associated with a third mode. Ifthe signal is associated with the first mode, the signal processingcomponent causes the switch to be modulated at a first frequency. If thesignal is associated with the second mode, the signal processingcomponent causes the switch not to be modulated. If the signal isassociated with the third mode, the signal processing component causesthe switch to be closed for a period of time.

According to another embodiment, the present invention provides a methodfor regulating a power converter. The method includes a step forreceiving a first voltage. The method also includes a step for receivinga second voltage. The method additionally includes a step for processinginformation associated with the first voltage and the second voltage.Additionally, the method includes a step for determining a signal basedon at least information associated with the first voltage and the secondvoltage. Further, the method includes a step for regulating a switch fora power converter based on at least information associated with thesignal. The determining a signal is based on at least informationassociated with the first voltage and the second voltage. If the firstvoltage is higher than a first threshold, the signal is associated afirst mode. If the first voltage is lower than a second threshold andthe second voltage is higher than a third threshold, the signal isassociated with a second mode. If the first voltage is lower than thesecond threshold and the second voltage is lower than the thirdthreshold, the signal to is associated with a third mode. The step ofregulating a switch for a power converter includes causing the switch tobe modulated at a first frequency if the signal is associated with thefirst mode. If the signal is associated with the second mode, the switchis not modulated. If the signal is associated with the third mode,causing the switch is closed for a period of time.

According to yet another embodiment, the present invention provides asystem for regulating a power converter. The system includes a signalprocessing component that is configured to receive a first voltage and asecond voltage, to process information associated with the first voltageand the second voltage, to determine a signal based on at leastinformation associated with the first voltage and the second voltage,and to send the signal to a switch for a power converter. The switch isregulated based on at least information associated with the signal. Thesignal processing component is configured to determine the signal to beassociated with a first mode, if the first voltage is higher than afirst threshold. If the first voltage is lower than a second thresholdand the second voltage is higher than a third threshold, the signal isassociated with a second mode. If the first voltage is lower than thesecond threshold and the second voltage is lower than the thirdthreshold, the signal is associated with a third mode. If the signal isassociated with the first mode, the signal processing component causesthe switch to be modulated at a first frequency. If the signal isassociated with the second mode, the signal processing component causesthe switch not to be modulated. If the signal is associated with thethird mode, the signal processing component causes the switch to bemodulated at a second frequency.

According to yet another embodiment, the present invention provides amethod for regulating a power converter. The method includes a step forreceiving a first voltage. The method also includes a step for receivinga second voltage. The method additionally includes a step for processinginformation associated with the first voltage and the second voltage.Also, the method includes a step for determining a signal based on atleast information associated with the first voltage and the secondvoltage. The method further includes a step for regulating a switch fora power converter based on at least information associated with thesignal. The step of determining a signal based on at least informationassociated with the first voltage and the second voltage includesdetermining various voltages. If the first voltage is higher than afirst threshold, the signal is associated a first mode. If the firstvoltage is lower than a second threshold and the second voltage ishigher than a third threshold, the signal is associated with a secondmode. If the first voltage is lower than the second threshold and thesecond voltage is lower than the third threshold, the signal isassociated with a third mode. If the signal is associated with the firstmode, the switch is modulated at a first frequency. If the signal isassociated with the second mode, the switch is not modulated. If thesignal is associated with the third mode, the switch is modulated at asecond frequency.

According to yet another embodiment, the present invention provides asystem for regulating a power converter. The system includes a signalprocessing component configured to receive a voltage, to processinformation associated with the voltage, and to determine a signal basedon at least information associated with the voltage, and to send thesignal to a switch for a power converter. The switch is regulated basedon at least information associated with the signal. If the voltage ishigher than a first threshold, the signal is associated with a firstmode. If the voltage is lower than a second threshold, the signal isassociated with a second mode. The signal processing component isconfigured to process information associated with the voltage, a thirdthreshold, and a fourth threshold, the third threshold and the fourththreshold being different. The signal processing component is furtherconfigured to determine a modulation frequency based on at leastinformation associated with the first voltage, the third threshold, andthe fourth threshold. If the signal is associated with the first mode,the signal processing component causes the switch to be modulated at themodulation frequency. If the signal is associated with the second mode,the signal processing component causes the switch not to be modulated.

According to yet another embodiment, the present invention provides amethod for regulating a power converter. The method includes a step forreceiving a voltage. The method also includes step for processinginformation associated with the voltage. The method additionallyincludes a step for determining a signal based on at least informationassociated with the voltage. The method further includes a step forregulating a switch for a power converter based on at least informationassociated with the signal. If the voltage is higher than a firstthreshold, the signal is associated a first mode. If the voltage islower than a second threshold, the signal is associated with a secondmode. The signal is determined based on at least information associatedwith the voltage further. The process of determining the signal includesprocessing information associated with the voltage, a third threshold,and a fourth threshold, the third threshold and the fourth thresholdbeing different. The process of determining the signal further includesa step for determining a modulation frequency based on at leastinformation associated with the first voltage, the third threshold, andthe fourth threshold. If the signal is associated with the first mode,the switch is modulated at the modulation frequency. If the signal isassociated with the second mode, the switch is not modulated.

It is to be appreciated that the present invention provides variousadvantages over conventional techniques. According to an embodiment, thepresent invention provides a more energy efficient solution as comparedto conventional techniques. For example, the present invention reducesthe numbers of transitions between on and off states of a power supply.According to another embodiment, the present invention offers a largewindow for power control and great flexibility. For example, more thanone threshold voltage threshold values are used in determining variousstates of the power supply. There are other benefits as well.

Various additional objects, features and advantages of the presentinvention can be more fully appreciated with reference to the detaileddescription and the accompanying drawings that follow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified diagram illustrating a burst mode operation of aconventional power system.

FIG. 2 is a simplified diagram illustrating a conventional burst modecontroller.

FIG. 3 is a simplified diagram illustrating a power system according toan embodiment of the present invention.

FIG. 4 is a simplified diagram illustrating a controller module for apower system according to an embodiment of the present invention.

FIG. 5 is a simplified diagram illustrating the operation of a powersystem according to an embodiment of the present invention.

FIG. 6 is a simplified flow diagram illustrating the operation of apower system according to an embodiment of the present invention.

FIG. 7 is a simplified timing diagram illustrating the operation of thepower control system according to an embodiment of the presentinvention.

In FIG. 8, the horizontal axis is used to represent the VFB voltagelevel and the vertical axis is used to represent the frequency of PWMswitching.

FIG. 9 is a simplified diagram illustrating logical components of aburst mode controller component according to an embodiment of thepresent invention.

FIG. 10 is a simplified diagram illustrating a supply voltage monitoraccording to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is related to integrated circuits. Morespecifically, the present invention can be applied to controllers usedfor switch mode power supply. According to various embodiments, thepresent invention provides various power control schemes to reducestandby power consumption and improves system efficiency. Merely by wayof example, the present invention can be used in switch mode powerconversion system including, among, other things, offline fly-backconverters and forward converters. It is to be appreciated that thepresent invention has a broad range of applications.

As mentioned above, various techniques have been developed for efficientpower systems. For example, conventional systems attempted to reduceswitching power due to core loss of transformers and inductors in apower system and power loss due to the snubber. Typically, power lossesare related with switching events. For example, high frequency switchingusually results in high switching power loss. Conventional techniquestypically attempt to reduce power loss by reducing switching frequency(e.g., use lower switching frequencies).

Unfortunately, low switching frequency can cause various designchallenges and problems. For example, low frequency switching designoften renders transform design difficult. According to a conventionaltechnique, to solve low frequency design problem, the switchingfrequency is adjusted according to the load. For example, high frequencyis used at heavy load, and low frequency used at light or no load. As aresult, the power loss that relates to frequency is reduced at light orno load condition maintaining. At the same time, a high frequencies atheavy load can be used if needed.

The frequency reduction usually improves power efficiency at light orzero load conditions, but often leads to other types of problems. Forexample, low frequencies can sometimes cause audio noise. When theswitching frequency is reduced to audio frequency range, the systemoften causes unavoidable and undesirable audible noise.

To improve power efficiency and reduce audio noise, various conventionalpower system utilizes burst mode techniques. Depending upon loadconditions, some PWM cycles are skipped and the operation of the powersystem becomes asynchronous.

FIG. 1 is a simplified diagram illustrating a burst mode operation of aconventional power system. This diagram is merely an example, whichshould not unduly limit the scope of the claims. One of ordinary skillin the art would recognize many variations, alternatives, andmodifications.

During a power on time (Ton) 110, a PWM signal turns on a power switchand forces the energy delivered to the load. During a power off time(Toff), a PWM signal turns off a power switch and stops energy frombeing delivered to the load. The switching frequency is above theaudible frequency range (i.e., greater than 22 KHz). Consequently, noaudible noise is generated. At the same time, standby power consumptionis reduced.

FIG. 2 is a simplified diagram illustrating a conventional burst modecontroller. This diagram is merely an example, which should not undulylimit the scope of the claims. One of ordinary skill in the art wouldrecognize many variations, alternatives, and modifications. For example,a burst control system 200 includes a burst mode controller 210 and aPWM controller 220. Both Ton and Toff signals from FIG. 1 are associatedwith the an error amplifier output (VFB) 230. When the load in a powersystem has small power demand, the VFB is at low voltage level. When theVFB voltage is less than a predetermined voltage level, the PWMcontroller 220 stops the switching operation. As a result, no energy isdelivered to the load, and the output voltage decreases. Typically, thedecreased output voltage level causes (i.e., by negative feedback) anincrease of the VFB voltage level. When VFB is greater than a secondpredetermined level, PWM controller 220 resumes the switching operation.By turning on and off the switching by the PWM controller, system powerconsumption is reduced.

Unfortunately, a conventional system as the burst control system 200often has various drawbacks. For example, temporary stop of switchingcan lead to slow response time. The stop of switching typically leads todrops for both output voltage and the power supply, and ultimatelycauses slow response time. For example, when the power supply dropsbelow an under-voltage lockout (UVLO) threshold, the PWM controller isturned off and a new startup cycle is initiated. A startup cycletypically takes up to seconds. During the startup cycle, the outputvoltage can be unregulated and fall off. To ensure that the outputvoltage remains regulated, it is often necessary to maintain the voltagesupply above the UVLO threshold voltage. Usually, a minimum duty cycle(i.e., a duty cycle of a predetermined period of time) of the PWM burstis required to maintain stability and energy balance of the powersupply. For example, the minimum duty cycle of the PWM is used todeliver a sufficient amount of energy to the power system and to keepthe voltage supply above the UVLO threshold voltage.

Therefore, it is to be appreciated that various embodiments of thepresent invention provide burst mode control schemes with extended rangeand higher efficiency. For example, during operation the burst modecontrol monitor monitors both the supply voltage VDD and the VFBvoltage. Among other things, a power system according to the presentinvention prevents the supply voltage from dropping below the UVLOthreshold voltage. At the same time, the power system maintains theadvantages (e.g., power efficiency, etc.) of the burst mode operation.

FIG. 3 is a simplified diagram illustrating a power system according toan embodiment of the present invention. This diagram is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. A power system 300 includes, among other things, acontroller module 310, a power supply 305, a primary winding 320, aswitch 322, an auxiliary winding 321, and an isolated feedback 330. Thecontroller module 310 is configured to control the output of the powersystem 300 based on, among other things, a current sensing (CS) signaland a VFB voltage.

FIG. 4 is a simplified diagram illustrating a controller module for apower system according to an embodiment of the present invention. Thisdiagram is merely an example, which should not unduly limit the scope ofthe claims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. The controller module 310includes a burst mode controller module 311, a PWM controller module314, a clock 312, an one-shot module 313, and a gate driver 316. Theburst mode controller module 311 receives inputs from both the output(i.e., the VFB signal) and the power supply (VDD). The PWM controllermodule 313 receives an input from the clock 312 (e.g., implemented by anoscillator), an input from the VFB signal, an input from the CS signal,and two inputs from the burst mode controller module 311.

Both the burst mode controller module 311 and the PWM controller module314 utilizes the VFB signal to monitor output of the power system. TheVFB signal is a feedback voltage that is related to the load of thesystem. For example, the VFB signal is a negative feedback voltage fromthe load. As another example, the VFB signal is a positive feedbackvoltage from the load. The PWM controller module 314 controls pulsewidth, which determines the amount of power to be transferred to theoutput, by comparing the VFB signal with the CS signal. According to aspecific embodiment, the burst mode controller module 311 is configuredto provide control signals to turn the PWM controller module 314 on oroff. For example, the VFB signal decreases in its amplitude under light(or zero) load condition, and the VFB signal increases in its amplitudeas load increases.

While in operation, the burst mode controller module 311 monitors boththe VFB and the VDD voltage level. For example, when the VFB signal islower than a threshold level, the burst mode controller module 311enters a burst mode. At the burst mode, the output of the PWM controllermodule 314 is disabled and the output from the gate driver 316 is alsodisabled. The switch 322 stays at an “off” state until the voltage ofVFB signal rises above a threshold voltages. For example, the voltage ofthe VFB signal rises due to an decrease in output voltage.

When the power has light or zero load, the VDD voltage is typically low.This is because the VDD voltage (as illustrated in FIG. 3) is suppliedby the auxiliary winding 312, which is electrically coupled to theoutput (i.e., the primary and secondary winding). According to aspecific embodiment, when the VDD voltage drops below a threshold level,the burst mode controller module 311 enables an one-shot signal. Forexample, the burst mode controller module 311 causes the one shot module313 to output a one-shot signal to the gate driver 316. As merely anexample, a one-shot signal enables a pulse with a predetermined durationso that the pulse provides enough energy for the VDD voltage level toremain above the threshold level. The one shot signal causes the powerswitch 322 to be at an “on” state, which allows the VDD voltage level tobe maintained. According to another specific embodiment, the burst mondecontroller module 311 turns PWM switching on until the VDD voltage levelrises above the threshold level.

Switching events of the power system are triggered by clock signalsgenerated by the clock 312. As shown in FIG. 4, the clock 312 isconfigured to receive the VFB signal and an output from the burst modecontroller module 311. For example, clock signals are characterized by aclock frequency. The clock frequency can be set to either high or lowfrequency. When the voltage of the VFB signal is lower (e.g., underlight or zero load condition) than a threshold voltage level, the powersystem operates in a burst mode and at a low switching frequency (i.e.,clock frequency is set to low). When the voltage of the VFB signal ishigher (e.g., under heavy load condition and/or when load increases)than the threshold level, the power system operates in the burst modeand at a high or normal frequency (i.e., clock frequency is high).

FIG. 5 is a simplified diagram illustrating the operation of a powersystem according to an embodiment of the present invention. This diagramis merely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. Merely by way of anexample, FIG. 5 illustrates the operation of the power system 300 inFIG. 3. As shown in FIG. 5, the embodiment of the present invention isimplemented with a two-dimensional control scheme. It is to be noted thetwo-dimension control scheme according to the embodiment is superior tothe conventional one-dimension control schemes.

A power system according to a specific embodiments operates in fourquadrants. The four quadrants are determined based on the VFB voltageand the VDD voltage. For example, the VFB voltage is the feedbackvoltage signal and the VDD voltage is the power supply voltage. It is tobe understood that the axes represent threshold voltages. For example,at the intersection of the two axes, both the VFB voltage and the VDDvoltage are non-zero and positive. According to a specific embodiment,the horizontal axis represents a threshold voltage for the VFB voltage.According to another embodiment, there could be more than one horizontalaxis if there are more than one threshold voltages for the VFB voltage.Similarly, the vertical access represents a threshold voltage for theVDD voltage.

In Quadrant I, the power system operates in normal operation mode. Forexample, both the VDD and VFB voltages are high, and the PWM switchingis turned on.

In Quadrant II, the VFB voltage is high while the VDD voltage is low.For example, PWM switching is turned on, even when the VDD voltage isvery low.

In Quadrant III, both the VFB voltage and the VDD voltages are low. Forexample, then a pulse is provided by the one-shot controller module(e.g., the one-shot controller module 313 in FIG. 4). As anotherexample, the switching of the power system is temporarily turned on bythe PWM controller module.

In Quadrant IV, the VFB voltage is low and the VDD voltage is high,which usually means that the load is very light or zero. For example, inresponse to light or zero load, the PWM switching is turned off tomaintain balance of the power system. As another example, the PWMswitching is operating at a much lower above-audible frequency when theVFB voltage is very low.

FIG. 6 is a simplified flow diagram illustrating operation of a powersystem according to an embodiment of the present invention. This diagramis merely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. For example, various stepsin the flow diagram can be added, removed, replace, repeated,overlapped, and partially overlapped.

At step 601, the system starts. For example, various components asillustrated in FIG. 3 are powered on and started. According to aspecific embodiment, logic and algorithms of various control componentsare properly initialized. According to another example, variouselectrical components are properly charged to desirable states.

At step 602, the system operates in normal operation mode. According toa specific embodiment, to operate in the normal operation mode, twoconditions are required. First, the supply voltage VDD must be greaterthan the sum of a UVLO(ON) voltage (e.g., under-voltage lockout voltage)and a Vth2 (i.e., a predetermined threshold voltage). Second, the VFBvoltage is greater than a threshold voltage V_bur_L (i.e., apredetermined threshold voltage for burst mode control). For example,when the system operates in normal operation mode, the power regulationis controlled by the PWM controller module 314 in FIG. 4. It is to beunderstood that required threshold voltages can be set according tospecific applications.

During operation, voltages levels of various components of the systemmay change. For example, the VFB voltages may move up or down. Asanother example, the supply voltage VDD may change.

At step 604, the system determines whether the supply voltage VDD isgreater than the sum of the UVLO(ON) voltage and a threshold voltageVth2 and whether the VFB voltage is less than the threshold voltageV_bur_L. Typically, when VFB voltage is less than the threshold voltageV_bur_L, the system is operating with light load and it is oftendesirable for the system to enter burst mode. For example, the systemtypically consumes less power during burst mode operation. If the supplyvoltage VDD is greater than the sum of the UVLO(ON) voltage and thethreshold voltage Vth2 and the VFB voltage is less than the thresholdvoltage V_bur_L, the system operates in burst mode, at step 605.According to a specific embodiment, the burst mode controller module 311in FIG. 4 provides a burst mode signal that causes the system to enterburst mode.

According to a specific embodiment, at step 605, the PWM switching isturned off and the system operates in burst mode. According to anotherembodiment, at step 605 the PWM switching is operated at a much lowerfrequency compared to the normal operation mode. Depending uponapplication, the system consumes less energy in burst mode when PWMswitching is turned off or operating at a lower frequency. During theburst mode operation, little or no energy is provided for the supplyvoltage VDD. As a result, the supply voltage VDD drops during the burstmode operation. For example, the burst mode controller module 311controls the burst mode operation of the system. According to a specificembodiment, the burst mode controller module 311 is configured to turnPWM switching on or off.

At step 606, the system determines whether the VDD voltage drops belowthe sum of the UVLO(ON) voltage and the threshold voltage Vth2. Forexample, the system cannot properly operate when the VDD is too low. Ifthe VDD voltage is below the sum of the UVLO(ON) voltage and thethreshold voltage Vth2, the system enters step 607. If the VDD voltageis above the sum of the UVLO(ON) voltage and the threshold voltage Vth2,the system enters step 608.

At step 607, energy is supplied cause the VDD voltage rise above the sumof the UVLO(ON) voltage and the threshold voltage Vth2. It is to beappreciated, by ensuring that VDD voltage is above the sum of theUVLO(ON) voltage and the threshold voltage Vth2, VDD would not dropbelow the UVLO(ON) voltage, which determines whether the power systemwould be restarted. According to a specific embodiment, the PWMswitching is enabled by either the PWM controller module 314 in FIG. 4,For example, PWM switching can also enabled by the burst mode controllermodule 311 that sends a signal that enables PWM switching. After the PWMswitching is enabled, the VDD voltage increases. The PWM switching stayson until in step 603 that the VDD voltage is greater than the sum of theUVLO(ON) voltage and the threshold voltage Vth2. As an example, as boththe load and the VDD voltage increases, the VFB voltage increases aswell. When the VFB voltage is larger than a V_bur_H voltage (i.e., apredetermined threshold voltage for burst mode control), the systemstops operating in burst mode and operates normal mode.

According to another embodiment, the one-shot controller module providesa pulse to the switch of the power system that causes the VDD voltage toincrease above the sum of the UVLO(ON) voltage and the threshold voltageVth2.

At step 608 (i.e., after it is determined that the VDD voltage is abovethe sum of the UVLO(ON) voltage and the threshold voltage Vth2), the VFBvoltage is compared with the V_bur_H voltage. If the VFB voltage ishigher than the threshold voltage V_bur_H (e.g., the load on the systemis heavy), the system stops operating in burst mode and operates innormal mode. On the other hand, if the VFB voltage is lower than theV_bur_H voltage, the system stays in the burst mode.

It is to be understood that FIG. 6 merely provides a specific example.There can be many variation, alternations, and modifications. Forexample, various threshold voltages

To further illustrate the operation of the power control system, FIG. 7is presented. FIG. 7 is a simplified timing diagram illustrating theoperation of the power control system. This diagram is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. For example, FIG. 7 illustrates the operation of thesystem 300 as shown in FIG. 3.

At T1, the system operates in normal mode (i.e., PWM switching is used).The VFB voltage is above the V_bur_H voltage, the supply voltage VDD isgreater than the sum of the UVLO(ON) voltage and the threshold voltageVth2, and the system operates in a normal mode (e.g., regular PWMswitching mode). For example, the system operates in the normal mode asdescribed in step 602 in FIG. 6. Depending upon applications, the PWMcontroller module 314 controls the PWM switching operation during thenormal operation mode.

Between T1 and T2, the system continues operating in the normal mode. AtT2, the system stops operating in the normal mode when the VFB voltagedrops below the V_bur_H voltage, which means that the load on the systemis light or small. For example, the system operates in burst mode toconserve energy. Depending upon applications, the system burst modecontroller module 311 in FIG. 4 controls the burst mode operation.

Between T2 and T3, the system continues operating in burst mode. Forexample, during the time between T2 and T3, the VDD voltage drops due tothe burst mode operation. At a certain time between T2 and T3, the VFBincreases. For example, additional loads are connected to the system.

At T3, VDD voltage drops below the sum of the UVLO(ON) voltage and thethreshold voltage Vth2. In response, the system turns on PWM switching.Depending upon application, the PWM operation is controlled by eitherthe PWM controller module 314 and/or the one-shot controller module 313as shown in FIG. 4.

Between T3 and T4, the PWM switching is on. For example, the PWMswitching stays on until the VDD voltage rises above the sum of theUVLO(ON) voltage and the threshold voltage Vth2, at T4. For example, theoperation of the system between T3 and T4 are illustrated in steps 607and 603 in FIG. 6. At T4, the system once again turns off PWM switchingand operates in burst mode to conserve energy. For example, burst modeoperation is controlled by the burst mode controller module 311 in FIG.4.

Between T4 and T5, the system operates in burst mode. At T5, the VFBvoltage rises above the threshold voltage V_bur_H. For example, the VFBvoltage increases due to an increase on the load that is connected tothe system. As an example, to be able to provide a sufficient amount ofenergy to the load, the system turns on PWM switching and resumes in thenormal operation mode.

It is to be appreciated that FIG. 7 merely provides an example, whichshould not unduly limit the scope of the claims. For example, the VDDand VFB voltages as shown in FIG. 7 merely provide an example of thesystem operation.

FIG. 8 is a simplified diagram illustrating a burst mode operationaccording to an embodiment of the present invention. This diagram ismerely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications.

In FIG. 8, the horizontal axis is used to represent the VFB voltagelevel and the vertical axis is used to represent the frequency of PWMswitching. Depending upon application, the PWM switching may operate intwo frequencies: normal frequency (i.e., Fosc_normal as shown in FIG. 8)and low frequency (i.e., Fosc_low as shown in FIG. 8). For example thelow frequency is still above the audible frequency range of 22 kHz.According to a specific embodiment, the PWM switching operates in twomodes: on and off.

The frequency and/or mode of PWM switching depends on the VFB voltage.As shown in FIG. 8, there are two threshold levels (i.e., Vth1 and Vth2as shown in FIG. 8) for the VFB voltage. According to an embodiment, adrop of VFB voltage to below the threshold voltage Vth1 causes the PWMswitching to stop operating in low frequency mode and to resumeoperating at the normal frequency.

There could be various way to implement the system described in FIGS. 3through 8. For example, the PWM controller module, the one shotcontroller module, and the burst mode controller module are implementedwith digital logical control devices. As another example, variouscomponents of the system are implemented with logical units. FIG. 8 is asimplified diagram illustrating a burst mode controller module accordingto an embodiment of the present invention. This diagram is merely anexample, which should not unduly limit the scope of the claims. One ofordinary skill in the art would recognize many variations, alternatives,and modifications.

According to a specific embodiment, the burst mode controller module isconfigured to turn the PWM controller module and the one-shot controllermodule on or off. For example, the burst mode controller module isimplemented with various logical components. According to a specificembodiment, a burst mode controller module 900 can be used as acomponent for the system 300 in FIG. 3. For example, the burst modecontroller module 900 is the same the burst controller module 311 inFIG. 4. According to certain embodiments, the logic control of the burstmode controller module is configured to perform the operationillustrated by FIG. 6.

FIG. 9 is a simplified diagram illustrating logical components of aburst mode controller component according to an embodiment of thepresent invention. As shown in FIG. 9, a burst mode controller module900 includes the following components: P1 1. a comparator 910;

-   -   2. a comparator 920;    -   3. a comparator 930;    -   4. a comparator 940;    -   5. a NAND gate 950;    -   6. a NAND gate 960;    -   7. a NAND gate 970;    -   8. an inverter 980;    -   9. an inverter 924;    -   10. an inverter 921;    -   11. a delay 990;    -   12. a delay 923; and    -   13. an OR gate 922.

The comparators 910 and 920 compare the VFB voltage with thresholdvoltages V_bur_L and V_bur_H. According to the embodiment, the NANDgates 970, 960, and 950, the OR gate 922, and the inverter 921, asshown, are used to provided logic output based on the VFB voltage andVDD voltage inputs. It should be understood that other implementationsare possible. For example, logic control function may be implementedwith XOR gates in combination with AND gates.

Based on the voltage level of the VFB voltage and VDD voltage inputs,the burst mode controller module 900 is able to determine whether thePWM switching should be turned on or off. For example, the burst modecontroller module determines the operation of PWM switching as shown insteps 604 and 608 as shown in FIG. 6.

The operation of the burst mode controller module can be demonstrated bythe following example. When the VFB input 912 is less than the V_bur_Hinput 911 and the VDD_sense input 915 is larger than the Vth_vdd_(—)1input 914, then the output of the inverter 921 is zero and the output ofthe inverter 980 is also zero. Since both the output of the inverter 921and the output of the inverter 980 are zero, the output of the OR gate922 is also zero, which disables PWM switching. On the other hand, ifthe VFB input 912 is less than the V_bur_H input 911 and the VDD_senseinput 915 is less than the Vth_vdd_(—)1 input 914, then the output ofthe inverter 921 is zero and the output of the inverter 980 is “1”. As aresult, the output of the OR gate 922 is “1”, which enables PWMswitching. When the VDD_sense input 915 is less than the Vth_vdd_(—)2, aone-shot controller module is enabled to generate a minimum pulse, whichprevents the VDD voltage from dropping below the UVLO threshold voltage.For example, the burst mode controller module 900 is configured toprovide necessary control signals to carry out the operation of thepower system as illustrated according to FIG. 6.

FIG. 10 is a simplified diagram illustrating a supply voltage monitoraccording to an embodiment of the present invention. This diagram ismerely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. According to a specificembodiment, the supply voltage monitor is used to implement thecomparator 930 in FIG. 9. For example, the comparator 930 is implementedin conjunction with a conventional under-voltage lockout (UVLO) circuit.For example, FIG. 10 illustrates a detailed circuit diagram of a supplyvoltage monitor 1002 and a UVLO circuit 1001. According to anembodiment, the UVLO circuit 1001 is configured to send out apower-on-reset (POR) signal (e.g., output of the inverter 1010) when thesupply voltage VDD is turned on. When the supply voltage VDD reaches apredetermined level (e.g., UVLO (OFF)), the ULVO circuit outputs a PORsignal so that the power system starts operating. When the supplyvoltage VDD drops below a threshold level, the operations of the powersystem is halted.

As seen in FIG. 10, a positive feedback loop is formed by the zenerdiodes 1017 and 1013, MOSFETs 1016, 1015, 1018, and 1023, a diode 1012,resistors 1011, 1019, and 1080. For example, after power on if the VDDvoltage 1030 increases to a predetermined level, the gate voltage of theMOSFET 1023 is turned on and the positive feedback loop is activated.The output of the MOSFET 1023 pulls down the gate voltage of the MOSFET1018, which causes the zener diode 1017 to be shorted. As a result, aPOR signal is provided. As an example, when the VDD voltage 1030 dropsto and/or below the ULVO threshold voltage, the MOSFET 1023 is turnedoff, and the positive feedback is activated, which causes the gate ofthe MOSFET 1018 to be pulled up to VDD voltage through resistor 1019,causing the power system to halt.

According to a specific embodiment, a resistor ladder is formed byresistors 1080 and 1011. By adjusting the relative ratio of these tworesistors and matching the transistor 1060 and 1023, the VDD_Cout signal1050 can be generated when the VDD voltage 1030 falls to the sum of UVLOthreshold voltage and the Vth2 voltage. For example, a voltage gap, withthe magnitude of the Vth2 voltage, is produced.

It is to be understood FIG. 10 illustrates a specific component of thepower system according to an embodiment of the present invention. Therecan be many alternations and variations. For example, various types ofdiodes, resistors, and gates can be used to implement the UVLO andcomparator circuits. There can be other structures as well.

According to an embodiment, the present invention provides a system forregulating a power converter. The system comprises a signal processingcomponent that is configured to receive a first voltage and a secondvoltage, to process information associated with the first voltage andthe second voltage, to determine a signal based on at least informationassociated with the first voltage and the second voltage, and to sendthe signal to a switch for a power converter. The switch is regulatedbased on at least information associated with the signal. The signalprocessing component is further configured to determine the signal to beassociated a first mode, if the first voltage is higher than a firstthreshold. If the first voltage is lower than a second threshold and thesecond voltage is higher than a third threshold, the signal processingcomponent determines the signal to be associated with a second mode. Ifthe first voltage is lower than the second threshold and the secondvoltage is lower than the third threshold, the signal processingcomponent determines the signal to be associated with a third mode. Ifthe signal is associated with the first mode, the signal processingcomponent causes the switch to be modulated at a first frequency. If thesignal is associated with the second mode, the signal processingcomponent causes the switch not to be modulated. If the signal isassociated with the third mode, the signal processing component causesthe switch to be closed for a period of time. For example, theembodiment can be illustrated according to FIG. 4.

According to another embodiment, the present invention provides a methodfor regulating a power converter. The method includes a step forreceiving a first voltage. The method also includes a step for receivinga second voltage. The method additionally includes a step for processinginformation associated with the first voltage and the second voltage.Additionally, the method includes a step for determining a signal basedon at least information associated with the first voltage and the secondvoltage. Further, the method includes a step for regulating a switch fora power converter based on at least information associated with thesignal. The determining a signal is based on at least informationassociated with the first voltage and the second voltage. If the firstvoltage is higher than a first threshold, the signal is associated witha first mode. If the first voltage is lower than a second threshold andthe second voltage is higher than a third threshold, signal to isassociated with a second mode. If the first voltage is lower than thesecond threshold and the second voltage is lower than the thirdthreshold, the signal to is associated with a third mode. The step ofregulating a switch for a power converter includes causing the switch tobe modulated at a first frequency if the signal is associated with thefirst mode. If the signal is associated with the second mode, the switchis not modulated. If the signal is associated with the third mode,causing the switch is closed for a period of time. For example, theembodiment invention can be illustrated according to FIGS. 5-6.

According to yet another embodiment, the present invention provides asystem for regulating a power converter. The system includes a signalprocessing component that is configured to receive a first voltage and asecond voltage, to process information associated with the first voltageand the second voltage, to determine a signal based on at leastinformation associated with the first voltage and the second voltage,and to send the signal to a switch for a power converter. The switch isregulated based on at least information associated with the signal. Thesignal processing component is configured to determine the signal to beassociated with a first mode, if the first voltage is higher than afirst threshold. If the first voltage is lower than a second thresholdand the second voltage is higher than a third threshold, the signal isassociated with a second mode. If the first voltage is lower than thesecond threshold and the second voltage is lower than the thirdthreshold, the signal is associated with a third mode. If the signal isassociated with the first mode, the signal processing component causesthe switch to be modulated at a first frequency. If the signal isassociated with the second mode, the signal processing component causesthe switch not to be modulated. If the signal is associated with thethird mode, the signal processing component causes the switch to bemodulated at a second frequency. For example, the embodiment can beillustrated according to FIG. 4.

According to yet another embodiment, the present invention provides amethod for regulating a power converter. The method includes a step forreceiving a first voltage. The method also includes a step for receivinga second voltage. The method additionally includes a step for processinginformation associated with the first voltage and the second voltage.Also, the method includes a step for determining a signal based on atleast information associated with the first voltage and the secondvoltage. The method further includes a step for regulating a switch fora power converter based on at least information associated with thesignal. The step of determining a signal based on at least informationassociated with the first voltage and the second voltage includesdetermining various voltages. If the first voltage is higher than afirst threshold, the signal is associated with a first mode. If thefirst voltage is lower than a second threshold and the second voltage ishigher than a third threshold, the signal is associated with a secondmode. If the first voltage is lower than the second threshold and thesecond voltage is lower than the third threshold, the signal isassociated with a third mode. If the signal is associated with the firstmode, the switch is modulated at a first frequency. If the signal isassociated with the second mode, the switch is not modulated. If thesignal is associated with the third mode, the switch is modulated at asecond frequency. For example, the embodiment can be illustratedaccording FIG. 6.

According to yet another embodiment, the present invention provides asystem for regulating a power converter. The system includes a signalprocessing component configured to receive a voltage, to processinformation associated with the voltage, and to determine a signal basedon at least information associated with the voltage, and to send thesignal to a switch for a power converter. The switch is regulated basedon at least information associated with the signal. If the voltage ishigher than a first threshold, the signal is associated a first mode. Ifthe voltage is lower than a second threshold, the signal is associatedwith a second mode. The signal processing component is configured toprocess information associated with the voltage, a third threshold, anda fourth threshold, the third threshold and the fourth threshold beingdifferent. The signal processing component is further configured todetermine a modulation frequency based on at least informationassociated with the first voltage, the third threshold, and the fourththreshold. If the signal is associated with the first mode, the signalprocessing component causes the switch to be modulated at the modulationfrequency. If the signal is associated with the second mode, the signalprocessing component causes the switch not to be modulated. For example,the embodiment can be illustrated according to FIG. 4.

According to yet another embodiment, the present invention provides amethod for regulating a power converter. The method includes a step forreceiving a voltage. The method also includes step for processinginformation associated with the voltage. The method additionallyincludes a step for determining a signal based on at least informationassociated with the voltage. The method further includes a step forregulating a switch for a power converter based on at least informationassociated with the signal. If the voltage is higher than a firstthreshold, the signal is associated a first mode. If the voltage islower than a second threshold, the signal is associated with a secondmode. The signal is determined based on at least information associatedwith the voltage further. The process of determining the signal includesprocessing information associated with the voltage, a third threshold,and a fourth threshold, the third threshold and the fourth thresholdbeing different. The process of determining the signal further includesa step for determining a modulation frequency based on at leastinformation associated with the first voltage, the third threshold, andthe fourth threshold. If the signal is associated with the first mode,the switch is modulated at the modulation frequency. If the signal isassociated with the second mode, the switch is not modulated. Forexample, the embodiment can be illustrated according to FIG. 6.

It is to be appreciated that the present invention provides variousadvantages over conventional techniques. According to an embodiment, thepresent invention provides a more energy efficient solution as comparedto conventional techniques. For example, the present invention reducesthe numbers of transitions between on and off states of a power supply.According to another embodiment, the present invention offers a largewindow for power control and great flexibility. For example, more thanone threshold voltage threshold values are used in determining variousstates of the power supply. There are other benefits as well.

Although specific embodiments of the present invention have beendescribed, it will be understood by those of skill in the art that thereare other embodiments that are equivalent to the described embodiments.Accordingly, it is to be understood that the invention is not to belimited by the specific illustrated embodiments, but only by the scopeof the appended claims.

1.-36. (canceled)
 37. A system for regulating a power converter, thesystem comprising: a signal processing component configured to receive avoltage, to process information associated with the voltage, and todetermine a signal based on at least information associated with thevoltage, and to send the signal to a switch for a power converter, theswitch being regulated based on at least information associated with thesignal; wherein the signal processing component is further configuredto: if the voltage is higher than a first threshold, determine thesignal to be associated a first mode; if the voltage is lower than asecond threshold, determine the signal to be associated with a secondmode; wherein the signal processing component is further configured to:process information associated with the voltage, a third threshold, anda fourth threshold, the third threshold and the fourth threshold beingdifferent; determine a modulation frequency based on at leastinformation associated with the first voltage, the third threshold, andthe fourth threshold; wherein: if the signal is associated with thefirst mode, the signal processing component causes the switch to bemodulated at the modulation frequency; if the signal is associated withthe second mode, the signal processing component causes the switch notto be modulated.
 38. The system of claim 37 wherein the voltage isassociated with a feedback voltage.
 39. The system of claim 37 whereinthe first threshold voltage and the second threshold voltage aredifferent.
 40. The method of claim 37 wherein the first threshold ishigher than the second threshold.
 41. The method of claim 37 wherein thefirst threshold is lower than the second threshold.
 42. A method forregulating a power converter, the method comprising: receiving avoltage; processing information associated with the voltage; determininga signal based on at least information associated with the voltage;regulating a switch for a power converter based on at least informationassociated with the signal; wherein the determining a signal based on atleast information associated with the voltage including: if the voltageis higher than a first threshold, determining the signal to beassociated a first mode; if the voltage is lower than a secondthreshold, determining the signal to be associated with a second mode;wherein the determining a signal based on at least informationassociated with the voltage further including: processing informationassociated with the voltage, a third threshold, and a fourth threshold,the third threshold and the fourth threshold being different;determining a modulation frequency based on at least informationassociated with the first voltage, the third threshold, and the fourththreshold; wherein the regulating a switch for a power converterincludes: if the signal is associated with the first mode, causing theswitch to be modulated at the modulation frequency; if the signal isassociated with the second mode, causing the switch not to be modulated.43. The method of claim 42 wherein the voltage is associated with afeedback voltage.
 44. The method of claim 42 wherein pulse-widthmodulation is performed when the signal is associated with a first mode.45. The method of claim 42 wherein the first threshold and the secondthreshold are the same.
 46. The method of claim 42 wherein the firstthreshold and the second threshold are different.